Many hams have two or more antennas. Traditionally, these antennas are brought into the shack an switched to the radio using either a manual antenna switch or a patch panel. Another option is to use a remote antenna switch mounted outside near the antennas with a single coax run back to the shack. An antenna controller in the shack is then used to select the active antenna. Most remote antenna switches offer some sort of proprietary control box to control their antenna switch. In many cases, a simple switch panel can be used.

CTR2 offers another option. The CTR2 Antenna Switch Controller (ASC) replaces the proprietary control box or switch panel and is integrated into the CTR2 ecosystem. This controller requires an external antenna switch such as a DX Engineering RR8B-HP to switch the RF circuit.

There are several advantages to this approach.

  • You don’t need to buy a proprietary switch controller. The ASC can be configured to interface with most remote antenna switches on the market.
  • Instead of just manually selecting an antenna on a control box, CTR2 can automatically select an antenna (or antennas) for each radio it controls. For instance you may choose to use your dipole for your HF radio and a VHF beam for your VHF radio. Both antennas share the same coax and are automatically selected when you select the radio in CTR2. To complete the antenna routing, another remote antennas switch controlled by the CTR2 Radio Antenna Switch Controller (RASC) automatically routes the common antenna port from the antenna switch to the selected radio.
  • Different antennas can be automatically selected as you switch to each band. Maybe you have a dipole for 80 and 40 meters but your vertical works better for 20 to 10, and you have a small yagi for 6 meters. Simply configure CTR2 to switch to each of these antennas when you select a band.
  • Phased arrays present a different problem. With two or more phased arrays, different antenna combinations are connected in parallel while others are grounded to “steer” the RF energy in the desired direction. Most remote antenna switches require a diode matrix to pull in specific antenna relay groups for each switch position. While this works, it’s not very flexible. The ASC solves this problem by allowing you to choose which antenna relays are selected. A simple click or two on the Antenna Select page changes this antenna combination. These combinations can also be assigned by band if needed.


The ASC schematic is shown below. Schematic files can be downloaded here.


The ASC uses the same logic decoder as the RJ45 Switch and RASC boards. J1 on this board connects to the same Antenna Switch Control connector on the HMI as the RASC. This is done using a multi-tap 10-conductor ribbon cable (a cable with three connectors).

The main difference between the ASC and the RASC is that where the RASC can only select 1 of 16 output relays, the ASC can select multiple output relays. This is done using latching relays instead of momentary relays as used on the RASC.

In operation, IC1, the CD4514 4-to-16 decoder IC decodes the four-bit address presented to its DATA_1 through DATA_4 inputs by the HMI and sets one of sixteen outputs HIGH when the STROBE pin is toggled from HIGH to LOW. The ASC differs from the RASC in that the INHIBIT pin on the ASC it tied to the STROBE pin through a small time delay network so a few milliseconds after the STROBE pin goes LOW, the INHIBIT pin goes low, enabling the output from the decoder to go HIGH.

The address determines the action taken by the ASC. Addresses 0 to 7 operate the Set coil on relays K1 to K8. Addresses 8 to 15 operate the Reset coils on these relays.

Using this scheme, the HMI can control the state of each relay by simply sending a Set or Reset command to the board. To clear all relays on HMI initialization, addresses 8 to 15 are sent sequentially to the board. Because latching relays are used, the relays “remember” their last state even when the power is off.


Like the RASC there are several strapping options for this board. The options you use will depend greatly on the remote antenna switch you are controlling.

Option 1 – Internal Power

JP1 is installed and JP2 is open if you want to power the internal relays from the HMI‘s primary power or from external power applied to the RASC. To power the ASC from the HMI, install JP4 on the HMI board to provide power to this board. This source is reverse diode protected current from this board can’t flow back to the HMI board.

NOTE: The HMI can be powered from any voltage from 9 to 72 volts (depending on the DC-DC converter installed) so this option should only be used when powering the HMI from a 12 volt nominal power supply.

Option 2 – External Power

The ASC can be powered from an external +12 VDC power source. To enable this option, remove JP1, install JP2, and install a 2.1mm x 5mm coaxial power jack at J4. You can also power the ASC from an externally mounted power jack by soldering a jumper from pin 1 of J4 to pin 2 or 3 (i.e. make pin 1 of JP2 ground) then connecting the external power jack to JP2 with (-) on pin 1 and (+) on pin 2 of JP2.

NOTE: When using both the ASC and the RASC, you only need to install the coaxial power jack on one of the boards. Set that board for external power (JP2 installed) and both boards for internal power (JP1 installed). Do not install JP4 on the HMI.

Option 3 – Output

The ASC is designed to accommodate different remote antenna switch configurations. Some require (+) voltage on their input to pull in their antenna relays while others require a ground on their input to pull in their antenna relays. Consult your switch’s documentation to determine which method they use.

Source (+12 VDC)

To source a (+12 VDC) voltage to your remote antenna switch, install a jumper between pins 1 and 2 on JP3 and use either the Internal or External Power options above to provide the +12 VDC power. Connect the return (ground) on your remote antenna switch to pin 2 of the terminal block so both systems have a common ground.

Sink (Ground)

To sink the external antenna relay’s inputs to ground, install a jumper between pins 2 and 3 on JP3. Connect the return (ground) on your remote antenna switch to pin 2 of the terminal block so both systems have a common ground.

External Power

Some remote antenna switches may require +12 VDC on a common pin and a ground to be applied on an input to pull in a relay. In this case, install a jumper between pins 1 and 2 on JP3 and a jumper on JP4. In this configuration, +12 VDC will appear on pin 2 of both TB1 and TB2.

Another option is to provide external voltage for the remote antenna switch. This would be desirable if your remote antenna switch requires a voltage other than +12 VDC. To do this, remove all jumpers on JP3 and install a jumper on JP4. Connect the external voltage to pin 2 of TB1 or TB2.

NOTE: If the external voltage is +12 VDC (nominal) you can use it to power the the internal relays on the RASC too. Just install a jumper between pins 1 and 2 on JP3. This jumper can be seen in the lead photo at the top of this blog.

Please feel free to contact me if you have questions about configuring the ASC or RASC for your remote antenna switch.

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